The shoulder remains one of the most complex joints in the human body. It is composed of the clavicle or collar bone, the scapula or shoulder blade and the humerus or arm bone. There are two important joints in the shoulder: the glenohumeral joint or the joint between the arm bone and the shoulder blade, and the acromioclavicular joint or the joint between the collar bone and the shoulder blade.
There are three layers in the glenohumeral joint of the shoulder. Each layer provides a specific function to the joint. The most superficial layer is the deltoid muscle. It is one of the main motors of glenohumeral motion. The next layer is the rotator cuff musculature. It is a series of four muscles which connect the humerus to the shoulder blade and contributes to the fine motions of the glenohumeral joint. Finally there is the glenohumeral capsular ligaments which are fibrous connections between the humerus and the scapula. They control the extent of motion between the humerus and the scapula.
When the shoulder is injured or the shoulder has surgery, there is a loss of separation between the three layers of the glenohumeral joint. This is caused by excessive scar formation between the layers. Furthermore, there can be shortening or contracture of each individual layer during the injury or surgery process. Both the contracture of each layer and the scar formation between the layers causes a loss of motion between the humerus and scapula. The same process can occur between the scapula and the clavicle as well as the scapula and the thorax or chest of the patient.
The glenohumeral joint is capable of three specific motions: 1. abduction and adduction; 2. internal and external rotation; and 3. flexion and extension. Every position of the glenohumeral joint is a combination of these motions. Abduction of the humerus causes it to move away from the midline whereas adduction moves it towards the midline. Internal rotation of the humerus causes the forearm to rotate towards the body when the humerus is held at the patient's side whereas external rotation causes the forearm to rotate away from the body when the humerus is held at the patient's side. Finally, flexion of the humerus causes it to move forward away from the body whereas extension causes the humerus to backward away from the body.
There are two forms of therapy to help patients gain range of motion in injured or surgically impaired joints with motion loss. The first is manual therapy, which is a stretching program requiring direct hands-on manipulation by a therapist with the express intent of increasing motion in the affected joint. The second is mechanical therapy, which is a specific medical device designed to allow the patient to stretch the joint without the help of a therapist. It has been shown that the use of mechanical devices to assist the patient in gaining range of motion are both helpful and highly desired as a technique to help avoid surgical treatment of joint motion loss.
Therefore it is known to provide apparatuses which increase the range of motion for a shoulder. However, improvements are always welcomed.